It is an object of the invention to dispose the exhaust gas silencer of the engine in its flow of cooling air in such a way that optimum cooling is achieved whilst, at the same time ensuring that the outer wall of the casing has a smooth design.
It is a further object of the invention, once the engine has been switched off and hence the flow of cooling air has been interrupted, to prevent too much radiant heat from being emitted by the exhaust gas silencer, which is still hot, into its surroundings.